1. Field of the Invention
This invention relates generally to gas generators, and more particularly to method of operating a downhole gas generator system that includes multiple independently controlled combustion chambers.
2. Description of Related Art
The following art defines the present state of this field:
Challacombe, U.S. Pat. No. 3,721,297, teaches a system for cleaning wells that includes a series of gas generating modules and explosive caps. The explosive caps are used for generating a series of repeated mild explosions and a series of pressure pulsations, which provides both repetitive shock and repetitive sustained fluid pulsations. The shock is required to break up and loosen various formations and materials formed in the well casing perforations and interstices of surrounding formation. The pulsations achieve repeated flow of the well fluid back and forth through the casing perforations and surrounding formation to thereby remove particles of plugging material that are loosened by the shock waves. The assembly of gas producing modules and explosive caps is interconnected in a string and arranged so that the burning or explosion of one element of the string will, itself, initiate the burning or explosion of the succeeding element, thus eliminating the need for multiple control lines for the desired sequential ignition.
Can, U.S. Pat. No. 4,382,771, teaches a gas and steam generator for use in generating electricity. The generator includes a linear series of combustion chambers wherein water in combination with combustible materials is burned. Each combustion chamber is provided with a reduced nozzle-type outlet for creating great pressures and temperatures within the respective chambers, and each combustion chamber being arranged for receiving combustible materials therein for burning thereof. The initial combustion chamber preferably receives a fuel-oxygen mixture at the inlet end thereof for ignition, with the products of the combustion being maintained at a high pressure and temperature by the restrictive nozzle-type outlet of the chamber. Steam and additional combustible materials are introduced at the nozzle outlet of the chamber for ignition and passage into a next stage combustion chamber whereby additional heat and force is produced for ultimate delivery of great power for a work operation.
Hill et al., U.S. Pat. No. 4,633,951, teaches multiple combustion gas generating units that each use rocket fuel type propellants disposed in a well casing at preselected depths. The well casing is filled with a compressible hydraulic fracturing fluid comprising a mixture of liquid, compressed gas, and propant material and precompressed to a pressure of about 1,000 psi (or more) greater than the fracture extension pressure at the depth of the zone to be fractured. At least one of the gas generating units is equipped with perforating shaped charges to form fluid exit perforations at the selected depth of the fracture zone. The gas generating units are simultaneously ignited to generate combustion gasses and perforate the well casing. The perforated zone is fractured by the rapid outflow of an initial charge of sand free combustion gas at the compression pressure followed by a charge of fracturing fluid laden with propellant material and then a second charge of combustion gas.
Tilmont et al., U.S. Pat. No. 8,387,692, teaches a downhole steam generation apparatus that includes an injection section, a combustion section, and an evaporation section. The injection section may include a housing, injector elements, and injector plate.
Ryan et al., U.S. Pat. No. 4,558,743, teaches a steam generator for producing steam in a well casing for injection into a borehole for use in secondary and tertiary recovery of hydrocarbons. Fuel is injected axially into a combustion chamber having a reduced orifice in the bottom thereof and oxygen is introduced tangentially from a plurality of ports in the top of the combustion chamber to create a stable vortex flame. A portion of the walls of the combustion chamber are formed from a porous, sintered stainless steel cylinder through which water is pumped to cool the walls of the chamber and to form steam. The combustion products are mixed with a water mist in a steam generating section to form steam.
Fox, U.S. Pat. No. 4,385,661, teaches an apparatus for generation of steam in a borehole. The system includes a feedback preheater for the fuel and water before entering the combustor assembly. First, combustion gases are conducted from the combustion chamber to locations in proximity to the water and fuel supplies. Secondly, both hot combustion gases and steam are conducted from the borehole back to the water and fuel supply. The water used for conversion to steam is passed in a countercurrent manner through a plurality of annular water flow channels surrounding the combustion chamber. In this manner, the water is preheated, and the combustion chamber is cooled simultaneously, thereby minimizing thermal stresses and deterioration of the walls of the combustion chamber. The water is injected through slotted inlets along the combustion chamber wall to provide an unstable boundary layer and stripping of the water from the wall for efficient steam generation. Pressure responsive doors are provided at the steam outlet of the combustor assembly. The module is positioned in the water flow channel to maintain a relatively constant, controlled temperature.
Griffin et al., U.S. 20040069245, teaches a steam generator for reacting a stoichiometric mixture of hydrogen and oxygen, and injecting water into the hot reaction gases. The generator includes a pilot ignition chamber, a combustion and evaporation chamber with reaction zone, an evaporation zone and outlet nozzle, and a catalytic afterburning chamber. The figure also illustrates the feed devices for supplying a fuel, an oxidizing agent and water.
Couto, U.S. 20110000666, teaches a gas generator which generates a vitiated steam, which is a mix of water steam with combustion gases. The device of this invention may also be attached in petroleum wells, making feasible the extraction of petroleum from the mature wells. The device includes a vaporization chamber attached to the combustion chamber of a rocket engine, said combustion chamber is externally involved by a cooling system, and the nozzle includes spray water injectors.
Other references included as a matter of general interest include the following: Tilmont, et al., U.S. 2011/0127036; Retallick, et al., U.S. Pat. No. 2008/0053655; Kraus et al., U.S. 2006/0000427; and Person, U.S. Pat. No. 1993/5,259,341. The above-described references are hereby incorporated by reference in full.
The prior art teaches the combustion of a fuel for the production of steam for injection into a petrochemical reservoir to force the petrochemicals out through a well or other access point. The prior art systems struggle, however, to adjust the amount of gas injected so that the formation pressure does not exceed the capabilities of the gas generator, especially in formations that are not very porous. The prior art does not teach a gas generator having multiple combustion chambers that can be independently controlled, so that the output of gasses can be controlled to not exceed predetermined pressures. The present invention fulfills these needs and provides further advantages as described in the following summary.